Re: [PATCH v2] mmc: sdhci-msm: Boost controller core clock

From	Ulf Hansson <ulf.hansson@linaro.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH v2] mmc: sdhci-msm: Boost controller core clock
Date	2015-12-16 11:20 +0100
Message-ID	<qGhlD-s9-15@gated-at.bofh.it> (permalink)
References	(1 earlier) <qrEka-6l9-1@gated-at.bofh.it> <qrKpz-1YN-3@gated-at.bofh.it> <qrYLT-2ND-11@gated-at.bofh.it> <qsRS2-598-11@gated-at.bofh.it> <qtnyy-1ks-3@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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[...]

>> It seems like a reasonable assumption that the controller can't cope
>> with a higher clock rate than 100 MHz as "input" clock. That would
>> then mean that there are different versions of the controller, as it
>> seems like for some version it's fine with 200MHz and for some 100MHz.
>>
>> According to the DT compatible strings, *one* version is currently
>> supported, "qcom,sdhci-msm-v4"...
>
> The same version of hardware is there 4 times. The difference is
> the maximum clock frequency supported by them is different. In
> downstream kernels we've handled this by trimming the frequency
> tables for the different controllers in the clock driver.
> Setting the clock to INT_MAX will make it run at 400MHz, which
> doesn't look to be supported by anything besides sdc1 on 8974ac.
>
>>
>> I see two viable solutions. One would be to limit the clock rate
>> depending on the version of the controller (new compatible strings
>> needs to be added). Another one would be to limit the clock rate by
>> using the existing DT binding for max-frequency, and thus do a
>> clk_set_rate(mmc->f_max) during probe.
>>
>
> I'd rather see that done via OPP tables in DT, but I suppose
> max-frequency is fine too. We'll need to use OPPs soon enough
> because there's a voltage associated with that frequency.
>
> In case you're wondering, the max frequency for sdc1 on 8974ac is
> 400MHz. If it's just a plain 8974pro then the max frequency is
> 200MHz. Otherwise, sdc2 maxes out at 200Mhz and sdc3 and sdc4 max
> out at 100MHz.
>

I think we have reached a consensus on the viable options.

As we haven't heard from Ivan, do someone want to send a patch for
this or shall we just revert $subject patch (which I can deal with)?

Kind regards
Uffe
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Re: [PATCH v2] mmc: sdhci-msm: Boost controller core clock Ulf Hansson <ulf.hansson@linaro.org> - 2015-12-16 11:20 +0100
  Re: [PATCH v2] mmc: sdhci-msm: Boost controller core clock "Ivan T. Ivanov" <ivan.ivanov@linaro.org> - 2015-12-16 12:50 +0100
    Re: [PATCH v2] mmc: sdhci-msm: Boost controller core clock Ulf Hansson <ulf.hansson@linaro.org> - 2015-12-16 14:50 +0100

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